On-site disposal of waste water (sewage) from single family residences and commercial establishments in areas with no conventional sewer system has conventionally been accomplished by a septic tank system. The anaerobic effluent discharged from the septic tank, after settling of the solids portion of the incoming waste water, is passed into a subsurface drain field for percolation into the surrounding soil. Such a system works satisfactorily if properly installed and if proper soil conditions for disposal of the effluent by the drain field exist. While most residential septic systems work with harmony between the septic tank and drain field, there are increasing numbers of drain field failures in commercial systems. Commercial systems where food preparation wastes are involved are particularly susceptible to failure. The high strength and grease content related to food preparation is beyond the capacity of the conventional septic system.
In such systems, heretofore, small treatment plants which make use of chemical and/or biological treatment schemes to render the effluent suitable for disposal have been suggested. These treatment plants usually are designed to replace the conventional septic system. Such treatment plants are generally prohibitively expensive to and generally not economically feasible for treatment of commercial sewage, as from restaurants, in rural and semi-rural areas.